1. Field of the Invention
The present invention relates to an ink set for ink-jet recording, a recording method, an ink cartridge, a recording unit and an ink-jet recording apparatus.
2. Related Background Art
Nowadays, the quality of ink-jet recording images has become almost equal to that of the silver salt photography. Meanwhile, in view of further improvement of fastness of the ink-jet recording images such as light fastness, it is being studied to use water-insoluble coloring materials such as pigments for all of inks used for multi-color image formation, for example, yellow (Y) ink, magenta (M) ink, cyan (C) ink and black (Bk) ink. The inventors of the present invention have found, however, that the quality of ink-jet images formed with such inks (all water-insoluble pigment inks) comes short of the silver halide photography level, and that further technical development is required-to obtain an ink-jet recording image of which quality is as high as that of silver salt photography by using such an ink set.
Accordingly, an object of the present invention is to provide an ink set of pigment inks suitable for forming high quality multi-color images with the ink-jet recording system where bleed between black image and adjoining color image is significantly alleviated.
Another object of the present invention is to provide an ink-jet recording method for forming a high-quality ink-jet recording image using the above-described ink set.
Still another object of the present invention is to provide a recording unit for forming a high-quality ink-jet recording image using the above-described ink set and an ink-jet recording apparatus.
According to a first aspect of the present invention, there is provided an ink set for ink-jet recording comprising an aqueous black ink and an aqueous color ink, wherein
the black ink comprises a carbon black as a coloring material having a-volume average particle diameter determined by dynamic light scattering of not less than 50 nm,
the color ink comprises a pigment as a coloring material having a volume average particle diameter determined by dynamic light scattering of not more than 60 nm, and an accumulative 90% particle diameter of volume particle size distribution of not more than 100 nm,
the volume average particle diameter of the carbon black is larger than that the pigment in the color ink, and wherein
the surface tension of the black ink is higher than that of the color ink.
According to another embodiment of the present invention, there is provided an ink set for ink-jet recording comprising at least inks of four colors of black, yellow, magenta and cyan, wherein
(a) the black ink comprises at least water and carbon black, and a volume average particle diameter of coloring material by a dynamic light scattering method is no less than 50 nm,
(b) yellow, magenta and cyan comprise at least water and organic pigment, a volume average particle diameter of coloring material by a dynamic light scattering method is not more than 60 nm, and accumulative 90% particle diameter of volume particle size distribution is not more than 100 nm,
(c) the volume average particle diameter of the coloring material in the black ink is larger than the volume average particle diameter of the coloring material in the color ink,
and a surface tension of the black ink is higher than that of the color ink.
According to another aspect of the present invention, there is provided an ink-jet recording method comprising the steps of,
(i) preparing the above-described ink set for ink-jet recording;
(ii) applying the black ink to recording medium; and
(iii) applying the color ink to recording medium.
According to still another aspect of the present invention, there is provided an ink cartridge comprising ink tanks accommodating inks of the above-described ink set respectively.
According to still another aspect of the present invention, there is provided a recording unit comprising ink tanks accommodating inks of the above-described ink set respectively, and ink-jet heads that discharge the black ink and the color inks respectively.
According to still another aspect of the present invention, there is provided an ink-jet recording apparatus comprising
ink tanks accommodating the inks of the above-described ink set respectively, and
ink-jet heads that discharge the black ink and the color inks respectively.
The present invention enables obtaining images with significantly improved water fastness, light fastness and gas fastness and with significantly alleviated bleed between abutting black and color regions of the image by using inks all containing pigments as the coloring material.